Abstract:

Apparatus and process for removing surface regions of a component. The
prior art involves removing surface regions of a metallic component by
means of electrochemical processes. The electrochemical process is
accelerated by the use of a current pulse generator.

Claims:

1-26. (canceled)

27. A process for removing a coating from a surface region of a
component,arranging the component and an electrode in an
electrolyte;electrically connecting the component, the electrode, and a
current generator;generating a pulsed current or pulsed voltage by the
current generator;forming a sequence of current/voltage pulses by a
plurality of different blocks with a block having a current pulse;
andcombining a plurality of current/voltage pulses in sequence during the
electrolytic coating removal;wherein a positive and a negative
current/voltage pulses are used for the electrolytic coating
removal;wherein a block is defined by a plurality of current pulses,
pulse duration, pulse interval, current level, and pulse shape,applying
at least a first block which includes at least two consecutives pulses of
the same polarity with an interval between the pulses, andapplying at
least a second block which includes at least two consecutive pulses of
the same polarity with an interval between the pulses,wherein the second
block is different at least in the current level compared to the first
block.

28. The process as claimed in claim 27, further comprises arranging an
ultrasound probe within the electrolyte such that ultrasound excitation
improves the hydrodynamics of the coating removal process and thereby
assists the electrochemical reaction, and

29. The process as claimed in claim 27, wherein a positive or a negative
potential is applied to the component to generate a base current or base
voltage.

30. The process as claimed in claim 27, wherein a block is matched to a
constituent of an alloy to be removed in order to boost the removal of
the constituent of the alloy.

31. The process as claimed in claim 27, wherein the coating removed is of
an MCrAIY, where M is an element selected from the group consisting of
iron, cobalt or nickel.

32. The process as claimed in claim 27, wherein a base current is
superimposed on the current pulses and/or the intervals.

33. The process as claimed in claim 27, wherein the current voltage pulse
is a square wave shape pulse.

34. The process as claimed in claim 27, wherein the current pulse is a
square wave shape pulse.

35. The process as claimed in claim 27, wherein the pulse times range from
1 to 10 milliseconds.

36. The process as claimed in claim 27, wherein a low base current during
the pulse sequences and during the intervals is used.

37. The process as claimed in claim 27, wherein the plurality of
current/voltage pulses are combined repeatedly.

38. A process for removing a coating from a surface region of a
component,arranging the component and an electrode in an
electrolyte;electrically connecting the component, the electrode, and a
current generator;generating a pulsed current or pulsed voltage by the
current generator;forming a sequence of current/voltage pulses by a
plurality of different blocks with a block having a current pulse;
andcombining a plurality of current/voltage pulses in sequence during the
electrolytic coating removal;wherein a block is defined by a plurality of
current pulses, pulse duration, pulse interval, current level, and pulse
shape,applying at least a first block which includes at least two
consecutives pulses of the same polarity with an interval between the
pulses, andapplying at least a second block which includes at least two
consecutive pulses of the same polarity with an interval between the
pulses,wherein the second block is different at least in the current
level compared to the first block.

39. The process as claimed in claim 38, further comprises arranging an
ultrasound probe within the electrolyte such that ultrasound excitation
improves the hydrodynamics of the coating removal process and thereby
assists the electrochemical reaction.

40. The process as claimed in claim 38, wherein a positive and a negative
current/voltage pulses are used for the electrolytic coating removal.

41. The process as claimed in claim 38, wherein a positive or a negative
potential is applied to the component to generate a base current or base
voltage.

42. The process as claimed in claim 38, wherein a block is matched to a
constituent of an alloy to be removed in order to boost the removal of
the constituent of the alloy.

43. The process as claimed in claim 38, wherein the coating removed is of
an MCrAIY, where M is an element selected from the group consisting of
iron, cobalt or nickel.

44. The process as claimed in claim 38, wherein a base current is
superimposed on the current pulses and/or the intervals.

45. The process as claimed in claim 38, wherein the current voltage pulse
is a square wave shape pulse.

46. The process as claimed in claim 38, wherein the current pulse is a
square wave shape pulse.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001]This application is the U.S. National Stage of International
Application No. PCT/DE03/00953, filed Mar. 21, 2003 and claims the
benefit thereof. The International Application claims the benefits of
German application No. 10215374.4 DE filed Apr. 8, 2002, and German
application No. 10259365.5 DE filed Dec. 18, 2002, all of the
applications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

[0002]The invention relates to an apparatus and a process for removing
surface regions of a component as described in the claims.

BACKGROUND OF THE INVENTION

[0003]Hitherto, components which have been coated with coatings of type
MCrAIY or ZrO2 have had the coating removed, for example, by acid
stripping in combination with sand blasting or by high-pressure water
blasting.

[0004]EP 1 122 323 A1 and U.S. Pat. No. 5,944,909 show examples of the
chemical removal of surface regions.

[0012]FIG. 2 shows a time curve of a current of a current pulse generator,
and

[0013]FIG. 3 shows a further time curve of a current from a current pulse
generator.

DETAILED DESCRIPTION OF THE INVENTION

[0014]FIG. 1 shows an apparatus 1 according to the invention. The
apparatus 1 comprises a vessel 4 in which an electrolyte 7 there is
arranged. An electrode 10 and a component 13 are arranged in the
electrolyte 7. The electrode 10 and the component 13 are electrically
connected to a current/voltage pulse generator 16. The component 13 is,
for example, a coated turbine blade or vane, the substrate of which is a
nickel- or cobalt- base superalloy, to which a metallic layer has been
applied to serve, for example, as a corrosion-resistant or anchoring
layer. A layer of this type in particular has the composition MCrAlY,
where M stands for an element iron, cobalt or nickel.

[0015]The coating has been corroded during use of the turbine blade or
vane 13. The surface region 25 which has been formed as a result (as
indicated by dashed lines) is to be removed by the process according to
the invention and the apparatus 1 according to the invention. It is also
possible for layer regions 25 which have been formed by corrosion,
oxidation or other forms of degradation to be removed from a component 13
which does not have a coating, these layer regions being in the vicinity
of the surface.

[0017]An ultrasound probe 19, which is operated by an ultrasound source
22, may optionally be arranged in the electrolyte 7. The ultrasound
excitation improves the hydrodynamics of the process and thereby assists
the electrochemical reaction.

[0018]FIG. 2 shows an example of a current/voltage curve of the
current/voltage pulse generator 16.

[0019]The current pulse signal or the voltage pulse is, for example,
square-wave (pulse shape) and has a pulse duration ton. Between the
individual pulses there is an interval of length toff. Furthermore,
the current pulse signal is defined by its current level Imax.

[0020]The current (Imax) which flows between the electrode 10 and the
component 13, the pulse duration (ton) and the pulse interval
(toff) have a significant influence on the electrochemical reaction
by accelerating the latter.

[0021]FIG. 3 shows an example of a series of current pulses 40 which are
repeated. A sequence 34 comprises at least two blocks 77. Each block 77
comprises at least one current pulse 40. A current pulse 40 is
characterized by its duration ton, the level Imax and its pulse
shape (square-wave, delta, etc.). Other important process parameters are
the intervals between the individual current pulses 40 (toff) and
the intervals between the blocks 77.

[0022]The sequence 34 comprises, for example, a first block 77 of three
current pulses 40 between each of which there is an interval. This is
followed by a second block 77, which has a higher current level and
comprises six current pulses 40. After a further interval, there then
follow four current pulses 40 in the opposite direction, i.e. with a
reversed polarity.

[0023]The sequence 34 is finished by a further block 77 of four current
pulses.

[0024]The sequence 34 can be repeated a number of times.

[0025]The individual pulse times ton are preferably of the order of
magnitude of approximately 1 to 10 milliseconds. The time duration of the
block 77 is of the order of magnitude of up to 10 seconds, so that up to
500 pulses are emitted in one block 77.

[0026]The application of a low potential (base current) both during the
pulse sequences and during the intervals is optionally possible.

[0027]The parameters of a block 77 are matched to a constituent of an
alloy which, by way of example, is to be removed in order to optimize the
removal of this constituent. This can be determined in individual tests.